Light emitting devices are expected to be developed into a wide range of fundamental light emitting devices and applications, for example, organic electroluminescent devices (hereinafter referred to as organic EL device) and inorganic-organic hybrid light emitting devices.
Organic EL devices are charge injection-type selfluminous devices utilizing luminescence produced upon recombination of electrons and holes arrived at the luminescent layer. Organic EL devices have been energetically developed since T. W. Tang et al. demonstrated in 1987 that a device with a thin film, composed of a fluorescent metal chelate complex and diamine-type molecules, stacked thereon exhibits luminescence with high brightness at low drive voltage.
Conventional organic fluorescent materials and organic phosphorescent materials as the luminescent material for the luminescent layer have a broader spectrum and a lower color purity as compared with inorganic fluorescent materials, and a color filter or a resonator structure should be used for color purity improvement purposes. The use of the color filter or the resonator structure poses problems, for example, lowered utilization efficiency of light produced by luminescence, dependency of luminescent color upon the viewing angle, and increased production cost.
In order to solve the above problems, the use of inorganic semiconductor crystals of nano size called quantum dots (QD) instead of conventional organic materials has been proposed (patent document 1: Japanese Translation of PCT Publication No. 522005/2005). QD is mixed with an organic host material (a binder component) in the luminescent layer and forms a luminescent matrix that is held between the electrodes and is formed within the luminescent layer. The quantum dots are divided into semiconductor fine particles of which the luminescent color is regulated by regulating the particle diameter and dopant-containing semiconductor fine particles. The former quantum dots, i.e., semiconductor fine particles, emit light at a wavelength determined by the size (particle diameter) thereof. On the other hand, the latter quantum dots, i.e, dopant-containing semiconductor fine particles, emit light having a luminescent color inherent in the dopant used. The semiconductor fine particles and the dopant-containing semiconductor fine particles each exhibit a spectrum having a narrow half-value width and a high color purity. In particular, in the former QD, the wavelength of light emitted from QD can be accurately and continuously regulated by regulating the particle diameter in the production of QD and can realize a wider range of color reproduction than the latter QD restricted by a luminescent color inherent in the dopant.